The following unstaged, unretouched, unPhotoshopped and otherwise legit photo was caught on film in New Zealand in 1951 by a photographer convinced he was documenting a flying saucer over Auckland.

The US Air Force later released its conclusion that the saucer was in fact a lenticular cloud. I've been unable to find out why the US Air Force deployed its analysts and/or was the definitive source. But were the Air Force analysts right? According to Wikipedia, lenticular clouds (Altocumulus lenticularis) are "stationary lens-shaped clouds that form in the troposphere, normally in perpendicular alignment to the wind direction." Here are a few examples:

Lenticular cloud above Reno, Nevada

Oxenhope, England

Mt. Ranier

Mt. Fuji

Seen from the International Space Station

The Dalles, Oregon

Wikipedia continues, "Because of their shape, they have been offered as an explanation for some Unidentified Flying Object (UFO) sightings."

So either that explains Winter 1951. Or Wikipedia is part of a same US Air Force coverup.